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Medical Microbiology lectures > L.9 Anaerobes > Flashcards

L.9 Anaerobes Flashcards

1
Q

What are obligate anaerobes?

A

Survive only in the absence of oxygen and obtain energy exclusively via fermentation

Oxygen is toxic to obligate anaerobes due to the absence of key detoxifying enzymes such as peroxidase, catalase, and superoxide dismutase.

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2
Q

What happens to obligate anaerobes when exposed to oxygen?

A

Inhibition or death

This is due to the lack of key detoxifying enzymes that would neutralize oxygen.

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3
Q

Name two examples of obligate anaerobes.

A
  • Clostridioides perfringens
  • Bacteroides fragilis

These organisms are known for their anaerobic metabolic processes.

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4
Q

What are facultative anaerobes?

A

Can use either respiration or fermentation and are able to grow in both aerobic and anaerobic conditions

This versatility allows them to thrive in various environments.

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5
Q

Name two examples of facultative anaerobes.

A
  • Escherichia coli
  • Staphylococcus aureus

These bacteria can adapt to the presence or absence of oxygen.

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6
Q

What are endogenous sources of anaerobes?

A
  • Gastrointestinal tract (especially colon)
  • Oral cavity (gingival crevices)
  • Skin (sebaceous glands and hair follicles)

These sources are part of the normal flora in humans.

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7
Q

What are exogenous sources of anaerobes?

A
  • Soil
  • Sewage
  • Aquatic environments

These are environmental reservoirs where anaerobes can be found.

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8
Q

What type of infections do anaerobes often cause?

A

Endogenous infections when mucosal barriers are breached

This typically occurs in situations such as trauma or surgery.

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9
Q

List some clinical clues of anaerobic infections.

A
  • Infections near mucosal surfaces
  • Presence of necrotic tissue or abscesses
  • Putrid (foul) odour
  • Gas formation in tissues (e.g., crepitus)
  • Polymicrobial infections
  • Negative culture despite strong clinical suspicion

These clues can help in diagnosing anaerobic infections, which may not always be detected through standard cultures.

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10
Q

True or False: Anaerobes can grow in the presence of oxygen.

A

False

Anaerobes are specifically adapted to anoxic environments.

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11
Q

Fill in the blank: Anaerobes obtain energy exclusively via _______.

A

[fermentation]

This process allows them to survive without oxygen.

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12
Q

What type of bacteria are Clostridioides species?

A

Gram-positive, spore-forming anaerobic bacilli

They are known for their ability to form spores under hostile conditions.

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13
Q

Under what conditions do Clostridioides spores germinate?

A

Favorable anaerobic conditions such as inside the human body

Spores can survive in the environment for weeks to months.

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14
Q

What is the most common human pathogen among Clostridioides species?

A

Clostridioides perfringens

Specifically, the Type A strain is the most prevalent.

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15
Q

Where can Clostridioides perfringens be found?

A

Vegetative cells in GI/GU tracts of humans and animals; spores in soil, sewage, and aquatic environments

This highlights their widespread presence in various ecosystems.

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16
Q

What conditions are required for the pathogenicity of Clostridioides perfringens?

A

Damaged tissue or necrosis, anaerobic environment, impaired blood supply, complex nutrients, presence of Calcium ions (Ca²⁺)

These factors facilitate the growth and toxin production of the bacteria.

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17
Q

What is the alpha (α) toxin produced by Clostridioides perfringens?

A

Lecithinase that breaks down phospholipids in cell membranes

It destroys PMNs (neutrophils), red blood cells, platelets, and muscle tissue.

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18
Q

What are some clinical infections caused by Clostridioides perfringens?

A

Wound & soft tissue infections, gastrointestinal infections, obstetric/gynecologic infections

Each category encompasses specific conditions and symptoms.

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19
Q

What are the symptoms of food poisoning caused by Clostridioides perfringens?

A

Watery diarrhea within 6–18 hours

This condition is often self-limiting, resolving in 1–2 days.

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20
Q

Fill in the blank: Clostridioides perfringens can cause _______ enteritis, a severe and rare intestinal infection.

A

necrotic

This type of infection is less common compared to food poisoning.

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21
Q

What is gas gangrene associated with Clostridioides perfringens?

A

Rapid tissue destruction, severe pain, crepitance from gas production

It is a form of clostridial myonecrosis.

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22
Q

True or False: Clostridioides perfringens can thrive in necrotic uterine tissue.

A

True

This is particularly relevant in cases of clostridial endometritis or septic abortion.

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23
Q

What is a common source of food poisoning from Clostridioides perfringens?

A

Ingestion of contaminated food with large numbers of vegetative C. perfringens (>10⁵ CFU/g)

Spores can survive cooking and germinate when food is improperly stored.

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24
Q

What is the function of α-toxin?

A

Lyses RBCs, platelets, WBCs, endothelial cells → increases vascular permeability, tissue necrosis, massive hemolysis

α-toxin is a phospholipase C / lecithinase.

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25
What type of toxin is β-toxin and what does it cause?
Pore-forming toxin (PFT); causes necrotic lesions in necrotizing enterocolitis, especially in infants ## Footnote Structurally similar to S. aureus β-toxin.
26
Which strains produce ε-toxin and what is its effect?
Produced by type B & D strains; increases vascular permeability, especially in CNS ## Footnote ε-toxin is a pore-forming toxin.
27
What is the primary function of ι-toxin?
Has ADP-ribosyltransferase activity; disrupts cytoskeleton ## Footnote ι-toxin is produced by type E strains.
28
What type of toxin is NetB and what is its significance?
Necrotic enteritis B-like toxin; important in avian necrotic enteritis ## Footnote NetB toxin is associated with necrotic enteritis in birds.
29
What is CPE and what does it cause?
Heat-labile enterotoxin; causes foodborne illness (diarrhea) ## Footnote CPE is released during sporulation in the gut.
30
What role does α-hemolysin play?
Contributes to cell lysis and inflammation ## Footnote α-hemolysin is a cytolysin.
31
What is the main disease caused by Clostridioides difficile?
Antibiotic-associated diarrhea and pseudomembranous colitis ## Footnote C. diff infections occur after suppression of normal colonic flora.
32
Who are the at-risk populations for C. difficile infection?
Elderly, hospitalized or long-term care residents, recent or long-term antibiotic users ## Footnote Specific antibiotics include cephalosporins, clindamycin, and fluoroquinolones.
33
True or False: C. difficile infections are primarily a concern in healthy individuals.
False ## Footnote C. difficile infections are especially relevant in the elderly and those with weakened immune responses.
34
Fill in the blank: C. difficile is a main cause of __________ associated diarrhea.
antibiotic ## Footnote The infection often follows antibiotic treatment that disrupts normal gut flora.
35
What is Toxin A (TcdA) classified as?
Enterotoxin ## Footnote Induces inflammation, fluid secretion, IL-8–mediated neutrophil infiltration
36
What is the primary effect of Toxin B (TcdB)?
Causes cell death via Rho GTPase inactivation → cytoskeletal collapse ## Footnote More potent cytotoxin
37
What type of toxin is Binary Toxin (CDT)?
ADP-ribosyltransferase ## Footnote Enhances adhesion and may promote severe disease in some strains
38
Which toxin is commonly detected by molecular assays?
Toxin B ## Footnote Detected using PCR techniques
39
What is the treatment for mild-moderate cases?
Metronidazole ## Footnote Less favored now compared to other treatments
40
What are the treatments for severe cases?
Oral Vancomycin or Fidaxomicin ## Footnote These are preferred for severe cases
41
What are the options for recurrent cases?
Probiotics and Fecal microbiota transplantation (FMT) ## Footnote These treatments aim to restore gut microbiota
42
What disease is caused by Clostridium botulinum?
Botulism ## Footnote Rare but severe neuroparalytic illness
43
What are the symptoms of botulism?
Blurred vision, dysphagia, facial weakness ## Footnote Affects cranial nerves
44
What are the types of botulism?
Foodborne, infant, or wound botulism ## Footnote Different modes of transmission
45
Which neurotoxins are common in human disease?
Toxins A, B, E ## Footnote These toxins are primarily linked to human cases
46
Which neurotoxins mainly affect animals?
C1, D, F, G ## Footnote Less common in human disease
47
What type of toxins are all botulinum toxins?
AB toxins ## Footnote Consist of Binding + Active components
48
What is the mechanism of action of botulinum toxins?
Block acetylcholine release → results in flaccid paralysis ## Footnote Target cholinergic nerve endings at the neuromuscular junction
49
How do botulinum toxins affect neurotransmitter release?
Act as zinc metalloproteases → cleave SNARE proteins ## Footnote Necessary for neurotransmitter release
50
What temperature adaptation do mesophilic strains have?
Grow at moderate temperatures (human body temp) ## Footnote Optimal growth conditions
51
What is a concern regarding psychrotolerant strains?
Grow at low temperatures ## Footnote Food safety concern, especially in refrigerated foods
52
What is the stability of botulinum toxins when it comes to heat?
Heat-sensitive: destroyed by boiling food for 10 minutes ## Footnote Important for food safety measures
53
What type of organism is Clostridioides tetani?
Obligate anaerobe ## Footnote Cannot survive in O₂-rich environments
54
How does Clostridioides tetani typically enter the body?
Via puncture wounds, contaminated objects (e.g., nails, thorns)
55
What has contributed to the rarity of tetanus disease?
Widespread immunization (tetanus toxoid)
56
What is the primary toxin produced by Clostridioides tetani?
Tetanospasmin
57
What are the two chains of tetanospasmin?
* Heavy chain (B) * Light chain (A)
58
What does the heavy chain (B) of tetanospasmin do?
Binds to neurons
59
What is the function of the light chain (A) of tetanospasmin?
Active site
60
What neurotransmitters does tetanospasmin inhibit?
* GABA * Glycine
61
What symptom is caused by the inhibition of GABA and glycine release?
Prolonged, rigid muscle spasms (e.g., lockjaw)
62
What type of bacteria is Bacteroides spp.?
Anaerobic Gram-negative bacilli (GNB)
63
Where is Bacteroides spp. commonly found as normal flora?
* Oral cavity * GI tract * Female genital tract
64
How do Bacteroides spp. outnumber E. coli in the colon?
1000:1
65
What is the most common anaerobe isolated in clinical labs?
Bacteroides spp.
66
What type of infections do Bacteroides spp. cause?
Endogenous infections following mucosal breach
67
What are common causes of endogenous infections by Bacteroides spp.?
* Trauma * Surgery (e.g., bowel perforation)
68
What is critical to the virulence of Bacteroides spp.?
Polysaccharide capsule
69
What types of abscesses are Bacteroides spp. associated with?
Polymicrobial abscesses (often abdominal/peritoneal)
70
How do facultative bacteria support anaerobes in infections involving Bacteroides spp.?
Reduce pO₂
71
What is common regarding antimicrobial resistance in Bacteroides spp.?
Antimicrobial resistance is common
72
What is a common treatment for Bacteroides infections?
Metronidazole
73
What are some virulence factors of Bacteroides spp.?
* Surface variation (polysaccharides, fimbriae, enterotoxin) * Hydrolytic enzymes (e.g., Hyaluronidase, Chondroitin sulfatase, DNase, Lipase, Protease, Neuraminidase)
74
What specimens are used for wound and soft tissue infections?
pus, tissue samples, muscle biopsy ## Footnote These specimens help identify anaerobic infections in wounds.
75
What specimens are used for food-borne infections?
faeces, food, gastric contents, vomitus, serum ## Footnote These samples are essential for diagnosing food-borne anaerobic infections.
76
What specimen is specifically used for C. difficile infections?
faecal specimen ## Footnote This is crucial for accurate identification of C. difficile.
77
What media is used for isolating anaerobic bacteria?
Blood agar + neomycin + metronidazole disc, CCEY agar for C. difficile ## Footnote Specific media support the growth of anaerobic bacteria.
78
What are the conditions for anaerobic incubation?
Strict anaerobic incubation, anaerobic chambers used ## Footnote These conditions are necessary to promote the growth of anaerobic organisms.
79
What is observed in direct microscopy for anaerobic infections?
GP rods with/without spores, 'boxcar-like' rods for C. perfringens, 'drumstick' appearance for C. tetani ## Footnote Microscopy aids in the preliminary identification of bacteria.
80
What tests are performed for basic identification on Day 2?
Gram stain, catalase test, hemolysis, anaerobic growth, metronidazole susceptibility, egg yolk agar tests ## Footnote These tests help narrow down the identity of the bacteria.
81
What does C. perfringens show in terms of hemolysis?
β-hemolysis ## Footnote This characteristic is important for differentiating it from other Clostridia.
82
What biochemical tests are used for C. perfringens identification?
Positive for glucose, maltose, sucrose, lactose gelatin; lecithinase positive, lipase negative ## Footnote These biochemical properties confirm the identity of C. perfringens.
83
What is the Nagler reaction used for?
To neutralize α-toxin activity of C. perfringens with specific antitoxin ## Footnote This test helps confirm the presence of C. perfringens.
84
What is a key characteristic of C. tetani?
Swarming, drumstick GPBs, catalase negative ## Footnote These features are critical for identifying C. tetani.
85
What toxins are detected in C. botulinum?
Toxin detection via ELISA or PCR on serum, feces, food ## Footnote This confirms the presence of botulinum toxin in suspected cases.
86
What are the key features of C. difficile?
GPBs with spores, horse manure odor, no hemolysis, anaerobic growth ## Footnote These characteristics assist in identifying C. difficile infections.
87
What is a crucial identification method for Bacteroides spp.?
Identified via MALDI-TOF ## Footnote This advanced technique allows for accurate identification of bacterial species.
88
What are the susceptibility characteristics of Bacteroides fragilis?
Resistant to bile, susceptible to metronidazole, rifampicin, erythromycin ## Footnote This susceptibility profile is important for treatment considerations.
89
Fill in the blank: C. perfringens is positive for _______ and negative for lipase.
lecithinase ## Footnote This biochemical characteristic helps differentiate it from other Clostridia.

Medical Microbiology lectures (17 decks)

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